Implement new Concept Exercise: string-formatting

Read the linked v3 concept-exercise documentation and the F# implementing instructions first. Then inspect the existing concept exercise example under languages/fsharp/exercises/concept/numbers, including its .meta/design.md and .meta/config.json, and check the implemented-exercises list in the concept README. Done means the string-formatting exercise follows that structure and covers the stated learning objectives and prerequisites.

This issue describes how to implement the string-formatting concept exercise for the F# track.

Getting started

Please please please read the docs before starting. Posting PRs without reading these docs will be a lot more frustrating for you during the review cycle, and exhaust Exercism's maintainers' time. So, before diving into the implementation, please read up on the following documents:

• The features of v3.
• Rationale for v3.
• What are concept exercise and how they are structured?

Please also watch the following video:

• The Anatomy of a Concept Exercise.

Goal

The goal of this exercise is to teach the student the basics of the Concept of Integral Numbers in F#.

Learning objectives

• Know how to use the ToString() method to convert any object to a string.
• Know how to use printf formatting on values of any type.
• Know what the benefit of printf formatting is over string concatenation.
• Know how to use default format strings to convert to standard output formats.
• Know how to use custom format strings to convert to custom output formats.
• Know how to combine strings using functions in the String module.
• Know of the StringBuilder type and when to use it.

Out of scope

Nothing.

Concepts

This Concepts Exercise's Concepts are:

• string-formatting: know how to use the ToString() method to convert any object to a string; know how to use printf formatting on values of any type; know what the benefit of printf formatting is over string concatenation; know how to use default format strings to convert to standard output formats; know how to use custom format strings to convert to custom output formats; know how to combine strings using functions in the String module; know of the StringBuilder type and when to use it.

Prequisites

This Concept Exercise's prerequisites Concepts are:

• strings: strings will be formatted.
• inheritance: knowing that each class derives from object and thus has built-in methods.

Any data types used in this exercise (e.g. datetimes) should also be added as prerequisites.

Hints

• String module: the String module.
• Formatting text: shows how to use the printf-family functions to format text.

The following links all use C# as their language, but are equally valid for F#:

• Formatting types: the available format types to use.
• Standard numeric format strings: lists the standard numeric format strings.
• Custom numeric format strings: describes how to define custom numeric format strings.
• Standard date and time format strings: lists the standard date and time format strings.
• Custom date and time format strings: describes how to define custom date and time format strings.
• String builder: shows how to use the string builder.

After

• String module: the String module.
• Formatting text: shows how to use the printf-family functions to format text.

The following links all use C# as their language, but are equally valid for F#:

• Formatting types: the available format types to use.
• Standard numeric format strings: lists the standard numeric format strings.
• Custom numeric format strings: describes how to define custom numeric format strings.
• Standard date and time format strings: lists the standard date and time format strings.
• Custom date and time format strings: describes how to define custom date and time format strings.
• String builder: shows how to use the string builder.

Representer

This exercise does not require any specific representation logic to be added to the representer.

Analyzer

This exercise does not require any specific logic to be added to the analyzer.

Implementing

To implement this exercise, please follow these instructions.

Help

If you have any questions while implementing the exercise, please post the questions as comments in this issue.